讀書筆記之View之孿生兄弟－SurfaceView

view可以滿足大部分的繪圖需求，但是在某些時候卻心有餘而力不足，特别在是需要頻繁重新整理的界面上，例如遊戲界面，會不斷阻塞主線程，進而導緻畫面卡頓。這個時候我們就需要使用surfaceview了。

SurfaceView的使用

雖然說SurfaceView的使用比view複雜，但是在使用SurfaceView的時候會有一套使用的模版代碼，大部分的SurfaceView繪圖操作都可以套用這樣的模版代碼來進行編寫。是以SurfaceView的使用會更加簡單。

1.建立SurfaceView

建立自定義的SurfaceView繼承自SurfaceView，并實作兩個接口－SurfaceHolder.Callback和Runnable,具體代碼結尾展示，通過實作這兩個接口，就需要在自定義的SurfaceView中實作接口的方法

2.初始化SurfaceView

在SurfaceView的構造方法中，需要對SurfaceView進行初始化，通常需要定義三個成員變量。

SurfaceHolder,Canvas,線程标志位mIsDrawing

初始化SurfaceHolder對象，并注冊SurfaceHolder的回調方法。

mHolder＝getHolder();

mHolder.addCallback(this);

如下時SurfaceView的一般套用模版

public class SurfaceViewTemplate extends SurfaceView
        implements SurfaceHolder.Callback, Runnable {

    // SurfaceHolder
    private SurfaceHolder mHolder;
    // 用于繪圖的Canvas
    private Canvas mCanvas;
    // 子線程标志位
    private boolean mIsDrawing;

    public SurfaceViewTemplate(Context context) {
        super(context);
        initView();
    }

    public SurfaceViewTemplate(Context context, AttributeSet attrs) {
        super(context, attrs);
        initView();
    }

    public SurfaceViewTemplate(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        initView();
    }

    private void initView() {
        mHolder = getHolder();
        mHolder.addCallback(this);
        setFocusable(true);
        setFocusableInTouchMode(true);
        this.setKeepScreenOn(true);
        //mHolder.setFormat(PixelFormat.OPAQUE);
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        mIsDrawing = true;
        new Thread(this).start();
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder,
                               int format, int width, int height) {
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        mIsDrawing = false;
    }

    @Override
    public void run() {
        while (mIsDrawing) {
            draw();
        }
    }

    private void draw() {
        try {
            mCanvas = mHolder.lockCanvas();
            // draw sth
        } catch (Exception e) {
        } finally {
            if (mCanvas != null)
                mHolder.unlockCanvasAndPost(mCanvas);
        }
    }
}
      

下面是簡單畫闆實作

public class SimpleDraw extends SurfaceView
        implements SurfaceHolder.Callback, Runnable {

    private SurfaceHolder mHolder;
    private Canvas mCanvas;
    private boolean mIsDrawing;
    private Path mPath;
    private Paint mPaint;

    public SimpleDraw(Context context) {
        super(context);
        initView();
    }

    public SimpleDraw(Context context, AttributeSet attrs) {
        super(context, attrs);
        initView();
    }

    public SimpleDraw(Context context, AttributeSet attrs,
                      int defStyle) {
        super(context, attrs, defStyle);
        initView();
    }

    private void initView() {
        mHolder = getHolder();
        mHolder.addCallback(this);
        setFocusable(true);
        setFocusableInTouchMode(true);
        this.setKeepScreenOn(true);
        mPath = new Path();
        mPaint = new Paint();
        mPaint.setColor(Color.RED);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeWidth(40);
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        mIsDrawing = true;
        new Thread(this).start();
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder,
                               int format, int width, int height) {
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        mIsDrawing = false;
    }

    @Override
    public void run() {
        long start = System.currentTimeMillis();
        while (mIsDrawing) {
            draw();
        }
        long end = System.currentTimeMillis();
        // 50 - 100優化部分，防止有時候繪制不那麼頻繁。
        if (end - start < 100) {
            try {
                Thread.sleep(100 - (end - start));
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    private void draw() {
        try {
            mCanvas = mHolder.lockCanvas();
            mCanvas.drawColor(Color.WHITE);
            mCanvas.drawPath(mPath, mPaint);
        } catch (Exception e) {
        } finally {
            if (mCanvas != null)
                mHolder.unlockCanvasAndPost(mCanvas);
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        int x = (int) event.getX();
        int y = (int) event.getY();
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                mPath.moveTo(x, y);
                break;
            case MotionEvent.ACTION_MOVE:
                mPath.lineTo(x, y);
                break;
            case MotionEvent.ACTION_UP:
                break;
        }
        return true;
    }
}